Italian authorities have seized a "mother ship" used to traffic illegal migrants across the Mediterranean and picked up about 200 Syrians fleeing the civil war in their homeland, officials said Thursday.

European Union and Italian patrol boats chased down the fishing boat with a crew of 15 that had been used to ferry the immigrants into international waters near the Sicilian coast, prosecutors and police said.

The vessel's crew had already transferred the refugees into a smaller boat for the final leg of their voyage. Italian police boats arrested 199 migrants, including 64 children, all of whom were Syrian.

The fishing boat was towed back to the port of Catania in Sicily. The seizure of the mother ship was a result of an investigation into the drowning of six migrants off Sicily in August, prosecutors said in a statement.

The smugglers are part of an Egyptian crime group, they said. The exact departure point of the fishing boat is yet unknown.

Thousands of migrants try to reach Italy's southern shores in summer, when Mediterranean waters are calm enough for smaller boats to make the crossing, usually from Libya or Tunisia.

Though most usually come from sub-Saharan Africa, this year many are fleeing the Syrian civil war or political turmoil in Egypt and other parts of North Africa.

Almost 9,000 migrants reached Italy by boat between 1 July and 10 August, the Italian interior ministry said.

In the 12 months up to 10 August, more than 24,000 migrants, compared with around 17,000 in the same period a year earlier, and almost 25,000 in the 12 months before that, the ministry said.

Most migrants are drawn by hopes of finding work in the EU and many do not remain in Italy.

Illegal migrants intercepted by Italian authorities are taken to state-run immigration centres. Some leave the often lightly guarded buildings to seek work, and those who remain and cannot prove that they are political refugees can be deported home.